Date: Tue, 15 Oct 2002 00:40:00 -0500
Reply-To: John Rodgers <j_rodgers@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <j_rodgers@CHARTER.NET>
Subject: Re: Some Comments on the Torque Wrench Discussion
Content-Type: text/plain; charset=us-ascii
I used to work for a regional airline in Atlanta back in the dim past.
The shop procedure that we were mandated to follow was to calibrate our
torque wrenches before each use. We had a big machine mounted on a wall
that was calibrated monthly by a specialist from somewhere who deals
with such things, and if our work ticket called for a job requiring the
use of a torque wrench we had to take the wrench to the calibration
machine, and pull torque on the machine. If the torgue wrench and the
torque gage on the torque machine were not in sync, the wrench could not
be used without being sent to be calibrated first. This was a double
check, and I expect prevented a lot of failures from occuring that may
have otherwise.
Another devise used was a Sweeney Wrench. It was a type of torque wrench
that had a chain drive like some shop overhead wenches. This thing was
mounted on the end of the crankshaft of an engine and was used to
tighten the propeller shaft nut to secure the propeller to the shaft. It
was gear driven for maximum mechanical advantage and looked sort of like
a double ring and pinion setup . But it absolutely dogged that propeller
down on that shaft.
John Rodgers
88 GL Driver
Frank Grunthaner wrote:
>
> The debate over the merits of clicker vs beam torque wrenches moves me to a
> few comments. In my experience, I have used 4 different types of torque
> wrenches: the trusty beam, the widely available adjustable clicker, the dial
> (actually a beam and gear mechanism as has been pointed out) and the fixed
> calibrated clicker.
>
> To begin, I've been wrenching bolts for more than 44 years, the last 43.8
> using a torque wrench. Most of that twisting has been done on automobiles
> ranging from American iron, through German alloys, through French mystery
> metals and on to Italian aluminum. My laboratory is often described as a
> stainless steel palace. The UHV hardware ranges in value from about $75,000
> to $1,500,000. The proper tightening of flanges is critical to avoid leaks
> which can trash the experiments. Our typical operating pressures are below
> 10(-10) torr. To achieve these pressures, the systems are baked for extended
> periods to peak temperatures of 235 C to 450 C. These thermal cycles are
> particularly stressful for bolt preloads on copper sealing systems. Bolt
> torque specs range from 14 foot pounds to 125 foot pounds. All bolts are
> silver plated for thread lubrication. Noone works in that lab with using a
> torque wrench on every bolt. Over the years, I've fired a few for just such a
> transgression.
>
> My advice is, however educated your hand or butt is, use the torque wrench.
> Cheap insurance. Remember, no single time job is nearly as expensive as the
> second or third redo to get it right.
>
> Now as to the torque wrench issue. As far as I'm concerned, the key problem
> here is calibration. Now the trusty beam and the disguised beam (dial) both
> rely on the basic material properties of the beam. Anybody anywhere can
> reestablish zero (bend the pointer or rotate the bezel). The adjustable
> clicker can lose its calibration all too readily. Heavy over torque beyond
> the click point. Sharp drop to concrete. Massive ingestion of oil, dust and
> dirt. The real problem is with the adjustability. With adjustment comes the
> need to calibrate often and well.
>
> Now, the best wrench I use (used the same type for more than 30 years) is the
> fixed calibration clicker. This wrench is available in a wide range of torque
> values. One wrench, one value. For the lab, we use about 6 different bolt
> sizes, so we maintain 3 sets of 6 different wrenches. Now these wrenches are
> not ratchet drives, but rather use a replaceable box, open, Allen or torx
> head. Used like a regular open or box end wrench. I have had these
> recalibrated and never had one go out of specification.
>
> For automotive wrenching, however, I use an adjustable clicker and a beam
> wrench. The beam is usually a PITA to get just where I need it, so I never
> (well almost) use it on an engine. Nope. I use it to calibrate the clicker. I
> have a 1/2 inch drive beam and a 3/8 inch dial. I have appropriate box square
> sockets to drive them with the 1/2, 3/8 or 1/4 inch drive adjustable clicker.
> Just before use, I set up the clicker to the torque I need, then on to
> the job.
>
> As part of this drill, I always clean the threads of any reused bolt by
> chasing it with a die. I always use a MoS2 thread lubricant on anything
> except exhaust manifold bolts. There I use a WS2 lubricant because of the
> temperatures.
>
> All the hardware I'm talking about are available from Craftsman, Mac, Snap-On
> or from McMaster-Carr.
>
> Just a comment,
>
> Frank Grunthaner
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